1. Field of the Invention
The present invention concerns automatic transmission devices for automotive vehicles.
2. Background Art
In conventional automatic transmissions, epicyclic gear trains are controlled by a hydraulic power circuit that actuates brake bands or multidisk clutches to effect ratio changes, the power circuit being controlled by either a hydraulic or an electronic control circuit responsive to drive torque, to rotary speed of the engine, and/or to the vehicle speed. The drive torque typically is sensed indirectly by detecting the position of the accelerator pedal.
In spite of fifty years of improvements, conventional automatic transmissions are still encumbered to some extent by their original disadvantages: great weight, high cost, mediocre efficiency, and poor performance of the vehicle compared with that obtainable with a manually operated gear box.
Moreover, in the modern motor vehicles, the power and transmission unit has to be as compact as possible. This often raises problems, especially in the case of front-wheel drive vehicles, more specifically if the engine comprises more than four cylinders and if the transmission device offers numerous ratios and/or is of the automatically shifted type, because, then, the transmission device is necessarilly more cumbersome.